CNG is increasingly common as a fuel
of choice for fleets; buses, service
vehicles, etc. however it can be very difficult or inconvenient to get a canister refilled. That is unfortunate because CNG is much safer than propane (which is readily available everywhere). CNG is lighter than air. So, if there is a leak, CNG floats harmlessly away while propane sinks and collects in the bilge
where it could be ignited and explode. Because CNG is so much lighter than propane, it must be stored at higher pressures (2500 psi versus 40 psi or so for propane).